Treatment for mites and lice in the rat

by "Matmor" in collaboration with Professor Nils Søli at Norges Veterinærhøgskole (The Norwegian Veterinary College) and the
Norwegian Fancy Rat Society (NTF)

This is the first part of a survey as published in the Norwegian Fancy Rat society's periodical Gnag, and part II as pre-print. Part III will
appear later.
Thanks to Sheila Sowter for helping
me sort out the "Norwenglish"! The spelling mistakes are my own...

Part I of III

From April 2004 up to and including April 2009 seven different users of The Norwegian
Fancy Rat Society (NTF)’s forum reported side effects from treatment for mites
and lice. Three of the seven cases resulted in one or more deaths. Probable signs of
poisoning (cramps, problems with coordination and balance) were observed in two cases.
In the third case symptoms were not observed but a young rat was found dead in its
cage on the morning after treatment. The dead rat was already weakened by the infestation of lice.
There were also postings about treatment resistant mites.

In a former survey for NTF1 infestations of lice and mites were the most
common causes for rat owners to seek veterinary advice. No drug for rats has
marketing approval, neither for treating lice, mites, nor other maladies. Considering the
seriousness of the side effects, users of NTF’s forum, Råttforum in Sweden and
Tamrotten in Denmark were asked to fill in anonymously a net based form with questions
about treatment for lice and rats. The form can be seen at http://matmor.info/usoek2.htm
(Norwegian version only). The prospective participants were asked to fill in the form regardless of treatment
outcome. It was explained that information about treatmens which are safe and effective is just as valuable
as information about lack of effect or side effects.

The survey had questions regarding

What kind of drugs are used against lice and mites in the rat

What side effects have been observed

Treatment resistant lice and mites

How the drugs were used

Ultimately our aim is to find safer and more effective treatments.

Results

The survey was open for a month. During this time we had 25 contributions representing
more than 368 rat courses of treatments. A rat course of treatment (RCT) was defined
as the full dosage intended to cure one rat. The number is somewhat uncertain:
”more than” because some of the contributors had used this wording in their replies.
Judging from the number of rats that were reported as ”cured”, and how many rats that
were reported ”not cured” there were actually ”more than” 395 rat courses of
treatment. Some of the contributors had had trouble understanding what was meant by
”rat course of treatment”, even if this was explained with examples on the form.

Nine of 25 replies had
information about side effects, two about failed cures.

The veterinary drugs were Advantage spot-on, Advocate spot on for cats, Frontline spot-on and spray, Ivomec injection, mixture and oral paste, Stronghold spot on 120 and 60 mg/ml. The percentage is calculated from 368 [and 395], see text in the paragraph above as to why two different values are given.

As no veterinary drug for rat has a marketing approval there are no officially
recommended treatment regimes. Even so the use of fipronil, ivermectin, selamectin,
and permethrin to combat lice and mites in the rat has been described in scientific
litterature. Concerning permethrin the use of dusting powder cannot be compared to
Exspot. The uptake would most certainly be very different. Otherwise the litterature
describes the use of drugs with a marketing approval for other species than rat.
We did not find any scientific literature about the use of Imidacloprid against lice
and mites in the rat. The recommendations are by Florida Rat and Mouse Club of
America in collaboration with a vet.

* Exspot was not recorded in the survey, only at NTF’s forum.
Dosages resulting in cramps or death have been marked in bold red print.

Part II

Part I (in the former issue of Gnag) concerned itself with the reported dosages. Part 2 is about the reported treatment intervals, side effects, and
dosages for rat pups/pregnant or nursing does.

According to the survey, the course of treatment sometimes consisted of one application only of Frontline, Ivomec, or Stronghold. The two drugs for lice
and mites for which treatment failed in the survey were Frontline and Stronghold (one report for each remedy). At NTF’s forum treatment failure was
reported for Ivomec. In all reports of poor efficacy the treatment was given the recommended number of times according to the listed sources.

Table 3: Number of applications per rat and interval

Veterinary drug

Survey

Recommendation

No. applications

Interval

No. applications

Interval

Source

Advantage

2

21 d

1 or more

-/30 d

2,7*

Advocate

2-3

21 d

1 or more

-/30 d

7*

Exspot

?(1)

?

1 or more

-/7-30 d

7*

Frontline

1-2

-/14 d

1 or more

-/28 d

5,7*

Ivomec

1-3

-/10 d

3

7-14 d

2, 3, 8

Stronghold

1-3

10-21

2 or more

14-30 d

2, 4 6

7 is for dog and cat. Advantage and Advocate is reported to protect against re-infestation by fleas
for three to four weeks. The treatment interval is set at 30 days if needed. Frontline is reported to
protect against ectoparasites (dog or cat) for four weeks.

The case of treatment failure for Frontline applied to the spray, not to the spot-on product. It is
possible that the spray dosage is too low to reach the necessary concentration to kill lice and mites when
treating large rats, see mg/m2 in table 3. Most likely it is the concentration of the drug in skin fat that
kills vermin, not the dose in mg/kg. (Square meter animal has been computed from Meeh’s formula.)

Table 4: Dosage of fipronil 1 spray per rat

Spray

Rat mg/kg

Rat mg/m2

Spray

Dog mg/kg

Dog mg/m2

100 g rat

12,5

65,7

10 kg dog

7,5-15

161-322

500 g rat

2,5

22,7

60 kg dog

7,5-15

293-585

Side effects

None of the participants in the survey used the ”other”-category for side effects. The reported side effects are mostly in accordance
with side effects observed in rats during toxicological testing, but diarrhea, for example, was not recorded. On the other hand the toxicological
reports do not mention nasal noises. This was reported by several contributors. It is impossible to say if the noises were due to stress, lowered
immunity, or increased secretion of mucous.

The survey did not report deaths connected to treatment. A search at NTF’s forum showed that in two of the three cases with resulting death,
an excessive dose was administered compared to the recommendations in Table 2.

The table below presents all reported side effects, both from the survey and from NTF’s forum.

NB! The number of rats refer to the survey only, not treatment mentioned in forum posts.

Side effects from skin and hairs were reported for Advantage (redness and necrosis, one report), Frontline spot-on solution
(redness, discolouration, and abscess, one report), Ivomec paste (redness and hair loss one report, overdose), and Stronghold
(discolouration one report). At NTF’s forum there was an additional report of a skin reaction to Stronghold: seborrhoeic eczema,
and one report of necrosis after the administration of Ivomec injection.

Cramps, imbalance, confusion, and agitation was reported for Frontline spot-on (cramps, imbalance, confusion one report, overdose),
for Frontline spray (confusion, agitation one report), and for Ivomec paste (agitation two reports, overdose in at least one report).
Additionally cramps, psychotic behaviour, and death was reported on NTF’s forum following administration of Exspot (overdose).
Cramps were also reported after administring Frontline spray, dosage unknown. More general side effects like tiredness and a low
appetite was reported for Advantage (one report of tiredness), Frontline spot-on (tiredness and poor appetite one report, overdose),
and Ivomec paste (tiredness and poor appetite one report, overdose, and lethargy one report).

Nasal noise was reported as side effect in four out of 25 reports. These reports addressed Advantage (two cases), Frontline spray
(one case), and Stronghold (one case).

Treatment of rat kittens

The survey did not ask for information on treatment of pregnant or nursing does. Most of the rats in the survey were above 5 weeks.
Only 26 RCT were registered in this category, but the kittens still represent 7% of the total number of rats. In rat kittens,
Frontline spray was registered with 14 rat courses of treatment, and with 12 RCT Stronghold spot-on. No side effects were reported
for rat kittens in the study. On the other hand there were reports of lethal side effects of Exspot (”rat kittens”) and Frontline
(a ”freshly acquired” rat) at NTF’s forum, no exact age given. According to the recommendations in Veterinærkatalogen none of the
drugs are contra-indicated for nurslings, although rat kittens are not mentioned. Conciveably rat kittens are more likely to
experience side effects from dermal treatment than dog, cat, sheep and horse, as dermal absoption from rat skin is generally higher
than for the larger mammals. On the other hand reproductive toxicity is frequently more closely studied in rats than in other mammals.

References

http://matmor.info/R8helse.htm

Florida RMCA (Rat and Mouse Club of America) http://ratguide.com/meds/

The Internet version of ”Felleskatalogen over preparater i veterinærmedisinen 2008-09” Oct. 1 st. 2009

Elimination of an Infestation of Rat Fur Mites (Radfordia ensifera) from a Colony of Long Evans Rats, Using the Micro-dot Technique for Topical Administration of 1% Ivermectin
Condo et al. Contemp Top Lab Anim Sci. 1998 Jan;37(1):58-61.